We have found a single locus two allele (D and d) genetic system which has a major influence on levels of erythrocyte 2,3-diphosphoglycerate (DPG) in the rat. This Dpg locus is closely linked to the beta globin (Hbb) locus in the rat. Our current work involves placing the Dpg locus, segregating for D and d, on an inbred genetic background. We have established that the LOU/Mn inbred strain is homozygous d, and we are now carrying out 12 generations of backcrossing to place D (along with d) on this same background. This animal model will then be used to study the effects of oxygen variation (as influenced by variation in DPG levels) on biological systems in the rat.